Importance of allergen-environment interactions in epidemic thunderstorm asthma

Abstract

Australia is home to one of the highest rates of allergic rhinitis worldwide. Commonly known as 'hay fever', this chronic condition affects up to 30% of the population and is characterised by sensitisation to pollen and fungal spores. Exposure to these aeroallergens has been strongly associated with causing allergic reactions and worsening asthma symptoms. Over the last few decades, incidences of respiratory admissions have risen due to the increased atmospheric concentration of airborne allergens. The fragmentation and dispersion of these allergens is aided by environmental factors like rainfall, temperature and interactions with atmospheric aerosols. Extreme weather parameters, which continue to become more frequent due to the impacts of climate change, have greatly fluctuated allergen concentrations and led to epidemic thunderstorm asthma (ETSA) events that have left hundreds, if not thousands, struggling to breathe. While a link exists between airborne allergens, weather and respiratory admissions, the underlying factors that influence these epidemics remain unknown. It is important we understand the potential threat these events pose on our susceptible populations and ensure our health infrastructure is prepared for the next epidemic.

Keywords: asthma; climate; fungal spore; pollen; pollen allergy.

Figure 1.

Aeroallergen scale bar.

Figure 2.

Visualisation of aeroallergens traversing the upper and lower airways. Intact pollens, due to their size, get stuck along the mucosal membrane of the upper airways, which induces allergies. Ruptured pollen particles are caught up in the airflow and able to travel deep into the lower airways, which triggers asthmatic symptoms.

Figure 3.

Hypothesised representation of airborne allergen levels during various climates and its impact on susceptible individuals. From left to right: dry and cold conditions lead to moderate pollen levels and mild allergy (a), dry and hot conditions lead to high pollen levels and acute allergy (b), thunderstorms lead to high pollen & fungal spore levels and acute allergy & asthma (c), wet and warm conditions lead to high fungal spore levels and acute allergy (d), wet and cold conditions lead to moderate fungal spore levels and mild allergy (e).

Figure 4.

Visualisation of epidemic thunderstorm asthma prevalence (a) and ryegrass distribution (b) in Australia. Epidemic thunderstorm asthma events are characterised by an influx of asthmatic symptoms brought about by severe weather changes and high atmospheric pollen loads. Ryegrass is a key allergenic grass species responsible for triggering asthmatic symptoms during epidemic thunderstorm asthma (ETSA). Numbers signify total ETSA events per state (a). Blue represents ryegrass density; pink represents reported locations of known ETSA events (b).